Modern combine harvesters are becoming bigger and bigger and are formed with increasingly wider cutting tables the width of which considerably exceeds that of the harvester itself. In threshing, large amounts of dust and clouds of particles generate in the area around the harvester, posing a considerable hazard to the engine operation and above all being a serious fire hazard. In order to reduce such hazards it is important that as much as possible of the harvest residues in the form of straw and husks are spread laterally and rearward of the harvester to the largest extent possible.
The husk discharge device that is connected to the harvester sieving unit has a width roughly speaking corresponding to that of the harvester itself, and usually said device should be arranged in such a manner that after the threshing operation it spreads the husk laterally and rearwards over an area essentially corresponding to the width of the cutting table. Also the straw chopping device, which is connected to the harvester straw shaking unit or threshing cylinder and which is located downstream therefrom has approximately the same width as the harvester itself and normally, it is arranged to cut the straw into small pieces after the threshing operation and spread the cut-up straw over an area behind the combine harvester that essentially corresponds to the husk spreading width. Following the spreading of the husk and the cut straw as indicated above, the husk and the straw are as a rule ploughed into the ground together.
If for various reason it is not desired to chop the straw in the straw chopping device but instead to deposit the straw in the form of strings on the ground behind the harvester for subsequent collection and baling at a later date and use as forage, straw-bedding material, etcetera, this could be achieved with the aid of a guide plate. In such cases, the guide plate preferably could be arranged to pivot between a first position, wherein it closes the inlet to the housing of the straw chopping device, thus effecting shunting or bypassing of the straw chopping device and allowing deposition of the unchopped straw in the form of strings, and a second position, wherein it exposes the inlet to allow cutting of the straw in the straw chopping device and spreading of the chopped straw.
From SE-C2-512 815 is known a combine harvester of the type defined above, wherein the straw chopping device is located downstream from not only the straw shaking unit or threshing cylinder but also from the husk discharge device. In this case, the guide plate is located between the husk discharge and straw chopping devices and it is movable between the above-defined positions for deposition of the straw in the form of strings and straw chopping. Irrespective of the position of the guide plate, the husk discharge opening in the blower house of the husk discharge device may be shifted between a first position, wherein the husks is made to spread across the ground, and a second position, wherein the husks may be mixed with the unchopped straw.
When the husk is to be mixed with the straw to be deposited in strings, this operation takes place with the guide plate assuming its first position and the husk discharge opening its second position whereas reversely, when the husks are to be mixed with the straw that is to be chopped, i.e. upstream from this straw chopping device, this operation takes place with the guide plate and the husk discharge opening assuming their respective second positions. In order to make possible admixture of the husk into the straw in the last-mentioned situation, the guide plate is formed with a husk through-passage that is arranged to be closed and opened. The passage is open, when the guide plate assumes its second position, allowing chopping of straw, and it is closed, when the plate assumes its first position, allowing string-deposition of the straw.
For various reasons, such as lack of space or because of different structural/functional solutions, it is very difficult, or even impossible, in some types of combine harvesters, to mount the husk discharge device in a manner allowing the husk without problems to be mixed with or be blown into the straw that is to be chopped in the straw chopping device upstream from said device.
In addition, particularly in the case of large volumes of husks (and boss) it may sometimes involve difficulties to satisfactorily and without unnecessary waste blow the husk out through the open through-passage in the guide plate and into the straw chopping device.
Furthermore, owing to the admixture of husk into the straw that is to be chopped, upstream from the straw chopping device, it may sometimes happen, for instance when large volumes of straw and husk are to be processed or when their moisture contents are high, that the straw chopping device is “overloaded” or becomes clogged. In turn, this situation may lead to impaired spreading of the chopped straw together with the likewise at least to some extent chopped, and even to breakdown.